Process for the copolymerization of ethylene

ABSTRACT

A process for producing a copolymer of ethylene containing from 0.1 to 99% by mol of one or more derived units of alpha-olefins of formula CH 2 ═CHA, wherein A is a C 2 -C 20  alkyl radical, comprising contacting, under polymerization conditions, ethylene and one or more alpha-olefins in the presence of a catalyst system obtainable by contacting: a) a metallocene compound of formula (I): wherein M is zirconium, titanium or hafnium; X, same or different, is a hydrogen atom, a halogen atom, or an hydrocarbon group; R 1 , is a hydrocarbon group; R 2  R 3 , R 4 , R 5  and R 6 , are hydrogen atoms or hydrocarbon groups; Q is a radical of formula (II), being bonded to the indenyl at the position marked by the symbol *; (II) wherein: T 1 , T 2 , T 3 , T 4  and T 5 , are carbon atoms (C) or nitrogen atoms (N); m 1 , m 2 , m 3 , m 4  and m 5  are  0  or  1 ; R 7 , R 8 , R 9 , R 10  and R 11  are hydrogen atoms or hydrocarbon groups; and b) an alumoxane or a compound capable of forming an alkyl metallocene cation.

The present invention relates to a process for the copolymerization ofethylene and one or more alpha-olefins of formula CH₂═CHA, wherein A isa C₂-C₂₀ alkyl radical, in the presence of a metallocene catalyst.

It is known that polyethylene can be modified by the addition, duringthe polymerization reaction, of small quantities of alpha-olefins,generally 1-butene, 1-hexene or 1-octene. This modification givesethylene copolymers which have short branches along the main chain dueto the units derived from the alpha-olefin comonomers. The branches havethe effect that the degree of crystallinity and hence the density of thecopolymer turn out to be lower than in polyethylene homopolymer.Typically, ethylene copolymers have densities of the order of0.915-0.940 g/cm³ associated to advantageous mechanical properties, inparticular for the production of films.

The lowering of the degree of crystallinity and of the density of thecopolymers depends on the type and quantity of the incorporatedalpha-olefin. In general, the greater the quantity of incorporatedalpha-olefin, the lower are the resulting degrees of crystallinity anddensity. Besides the type and quantity of the incorporated alpha-olefincomonomer, the properties of the copolymer depend on the distribution ofthe branches along the polymer chain. In particular, a uniformdistribution of the branches has relevant effects on the properties ofthe copolymers. In fact, with the same type and quantity of incorporatedalpha-olefin, a higher uniformity of distribution allows lower degreesof crystallinity and density to be obtained. Metallocene compoundshaving two bridged cyclopentadienyl groups are known as catalystcomponents for the homo- and copolymerization reaction of ethylene. Amain drawback of the use of metallocene catalysts is that the comonomerincorporation ability is quite low, and therefore it is necessary to usea large excess of comonomer in order to achieve copolymers having thedesired comonomer content. Moreover it is often difficult to tune thecomonomer content in a copolymer.

Bis indenyl metallocene compounds having the indenyl moietiessubstituted in 4 position with a substituted phenyl group are known, forexample, in WO 98/40331, but they have never been used for obtainingethylene copolymer.

Thus it would be desirable to find a metallocene catalyst having animproved balance of properties, i.e. a good comonomer incorporationability in such a way that it is possible to use a small excess ofcomonomer in the reactor, maintaining at the same time a gooddistribution of the comonomer in the molecular chain so to achievepolymer having lower Tg. Moreover, the same time, the metallocenecatalyst should produce copolymers having high molecular weight.

According to an aspect of the present invention, it is provided aprocess for producing a copolymer of ethylene containing from 0.1 to 99%by mol of derived units of one or more alpha-olefins of formula CH₂═CHA,wherein A is a C₂-C₂₀ alkyl radical and optionally up to 5% by mol of apolyene, comprising contacting, under polymerization conditions,ethylene, one or more alpha-olefins and optionally said polyene, in thepresence of a catalyst system obtainable by contacting:

a) a metallocene compound of formula (I):

wherein

M is zirconium, titanium or hafnium; preferably M is zirconium orhafnium; more preferably M is zirconium;

X, equal to or different from each other, is a hydrogen atom, a halogenatom, a R, OR, OR′O, OSO₂CF₃, OCOR, SR, NR₂ or PR₂ group, wherein the Rsubstituents are linear or branched, saturated or unsaturatedC₁-C₂₀-akyl, C₃-C₂O-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl,C₇-C₂₀-arylalkyl radicals, optionally containing one or more heteroatomsbelonging to groups 13-17 of the Periodic Table of the Elements; and theR′substituent is a C₁-C₄₀-alkylidene, C₆-C₄₀-arylidene,C₇-C₄₀-alkylarylidene or C₇-C₄₀-arylalkylidene; preferably X is ahalogen atom, a R, OR′O or OR group; more preferably X is chlorine ormethyl;

R¹, equal to or different from each other, is a linear or branchedC₁-C₂₀-alkyl radical; preferably R¹ is a linear C₁-C₁₀-alkyl radicalmore preferably it is methyl or ethyl;

R², equal to or different from each other, is a hydrogen atom or alinear or branched, saturated or unsaturated C₁-C₂₀-alkyl radical;

R³ and R⁴, equal to or different from each other, are hydrogen atoms orlinear or branched, saturated or unsaturated C₁-C₂₀-alkyl,C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkylradicals, optionally containing one or more heteroatoms belonging togroups 13-17 of the Periodic Table of the Elements; or they can formtogether a condensed saturated or unsaturated 5 or 6 membered ring,optionally containing one or more heteroatoms belonging to groups 13-16of the Periodic Table of the Elements, said ring optionally bearing oneor more substituents; preferably R³ and R⁴ are hydrogen atoms, methylgroups or they form a condensed saturated or unsaturated 5 or 6 memberedring; R⁵ and R⁶, equal to or different from each other, are hydrogenatoms or linear or branched, saturated or unsaturated C₁-C₂₀-alkyl,C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl, or C₇-C₂₀-arylalkylradicals, optionally containing one or more heteroatoms belonging togroups 13-17 of the Periodic Table of the Elements; or they can formtogether a condensed saturated or unsaturated 5 or 6 membered ring,optionally containing one or more heteroatoms belonging to groups 13-16of the Periodic Table of the Elements, said ring optionally bearing oneor more substituents; preferably R⁵ and R⁶ are C₁-C₂₀-alkyl orC₆-C₂₀-aryl radicals; more preferably they are methyl or phenyl;

Q is a radical of formula (II), which is bonded to the indenyl at theposition marked by the symbol *;

wherein

T¹, T², T³, T⁴ and T⁵, equal to or different from each other, are carbonatoms (C) or nitrogen atoms (N);

m¹, m², m³, m⁴ and m⁵ are 0 or 1; more precisely each of m¹, m², m³, m⁴and m⁵ is 0 when the correspondent T¹, T², T³, T⁴ and T⁵ is a nitrogenatom and it is 1 when the correspondent T¹, T², T³, T⁴ and T⁵ is acarbon atom; R⁷, R⁸, R⁹, R¹⁰ and R¹¹, equal to or different from eachother, are hydrogen atoms or linear or branched, saturated orunsaturated C₁-C₂₀-alkyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl,C₇-C₂₀-alkylaryl, C₇-C₂₀-arylalkyl radicals, optionally containing oneor more heteroatoms belonging to groups 13-17 of the Periodic Table ofthe Elements; or they can form together a condensed saturated orunsaturated 5 or 6 membered ring, optionally containing one or moreheteroatoms belonging to groups 13-16 of the Periodic Table of theElements; said rings can bear one or more substituents; with theprovisos that at least one of R⁷, R⁸, R⁹, R¹⁰ and R¹¹ is different fromhydrogen atom, and that no more than two of T¹, T², T³, T⁴ and T⁵ arenitrogen atoms;

b) an alumoxane or a compound capable of forming an alkyl metallocenecation; and optionally

c) an organo aluminum compound.

In a preferred embodiment, R⁹ is a linear or branched, saturated orunsaturated C₁-C₂₀-alkyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl,C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkyl radical; and R⁷, R⁸, R¹⁰ and R¹¹are hydrogen atoms.

In another preferred embodiment R⁸ and R¹⁰ are a linear or branched,saturated or unsaturated C₁-C₂₀-akyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl,C₇-C₂₀-alkylaryl, C₇-C₂₀radicals; and R⁷, R⁹ and R¹¹ are hydrogen atoms;

A preferred radical belonging to formula (II) has formula (IIa) beingbonded to the indenyl at the position indicated by the symbol *:

wherein

R⁹ is a branched, saturated or unsaturated C₁-C₂₀-alkyl or C₆-C₂₀-arylradical; more preferably R⁹ is a phenyl group, optionally substitutedwith one or more C₁-C₁₀ alkyl groups, or a group of formula C(R¹²)₃wherein R¹², same or different, is a linear or branched, saturated orunsaturated C₁-C₆-alkyl radical; preferably R¹² is methyl.

A further preferred radical belonging to formula (II) has formula (IIb)being bonded to the indenyl at the position indicated by the symbol *:

wherein

R⁸ and R¹⁰ are a branched, saturated or unsaturated C₁-C₂₀-alkyl or aCF₃ radical; more preferably they are a group of formula C(R¹²)₃ whereinR¹² has been described above;

R⁹ is a hydrogen atom or a linear or branched, saturated or unsaturatedC₁-C₂₀-alkyl or C₆-C₂₀-aryl radical optionally containing one or moreheteroatoms belonging to groups 13-17 of the Periodic Table of theElements; preferably R⁹ is a hydrogen atom.

A further preferred radical belonging to formula (II) has formula (IIc)being bonded to the indenyl at the position indicated by the symbol *:

wherein

at least one among R⁸, R⁹, R¹⁰ and R¹¹ is different from a hydrogenatom; preferably R¹⁰ and R¹¹ are hydrogen atoms; preferably R⁸ and R⁹are a linear or branched, saturated or unsaturated C₁-C₂₀-alkyl radical,or they form a saturated or unsaturated condensed 5 or 6 membered ringoptionally containing one or more heteroatoms belonging to groups 13-16of the Periodic Table of the Elements, said ring optionally bearing oneor more substituents; more preferably R⁸ and R⁹ form a saturated orunsaturated condensed 5 or 6 membered ring optionally containing one ormore heteroatoms belonging to groups 15-16 of the Periodic table;

A further preferred radical belonging to formula (II) has formula (IId),being bonded to the indenyl at the position indicated by the symbol *:

wherein:

R¹⁰ and R¹¹ are a linear or branched, saturated or unsaturatedC₁-C₂₀-alkyl radical, or they form a saturated or unsaturated condensed5 or 6 membered ring optionally containing one or more heteroatomsbelonging to groups 13-16 of the Periodic Table of the Elements, saidring optionally bearing one or more substituents; more preferably R¹⁰and R¹¹ form a saturated or unsaturated condensed 5 or 6 membered ringoptionally containing one or more heteroatoms belonging to groups 15-16of the Periodic table; such as phenyl ring, pyrrole ring, piridine ring;

said catalyst system further comprising:

Preferably the metallocene compound of formula (I) is in the racemicform. Non limitative examples of compound sof formula (I) are:

Wherein W and W′ are methyl or ethyl radicals.

Compounds of formula (I) are well know in the art. They can be prepared,for example, as described in to WO 98/40331.

Alumoxanes used as component b) can be obtained by reacting water withan organo-aluminium compound of formula H_(j)AlU_(3-j) orH_(j)Al₂U_(6-j), where the U substituents, same or different, arehydrogen atoms, halogen atoms, C₁-C₂₀-alkyl, C₃-C₂₀-cyclalkyl,C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkyl radical, optionallycontaining silicon or germanium atoms, with the proviso that at leastone U is different from halogen, and j ranges from 0 to 1, being also anon-integer number. In this reaction the molar ratio of Al/water ispreferably comprised between 1:1 and 100:1.

The molar ratio between aluminium and the metal of the metallocenegenerally is comprised between about 10:1 and about 30000:1, preferablybetween about 100:1 and about 5000:1. The alumoxanes used in thecatalyst according to the invention are considered to be linear,branched or cyclic compounds containing at least one group of the type:

wherein the substituents U, same or different, are described above.

In particular, alumoxanes of the formula:

can be used in the case of linear compounds, wherein n¹ is 0 or aninteger of from 1 to 40 and the substituents U are defined as above, oralumoxanes of the formula:

can be used in the case of cyclic compounds, wherein n² is an integerfrom 2 to 40 and the U substituents are defined as above.

Examples of alumoxanes suitable for use according to the presentinvention are methylalumoxane(MAO), tetra-(isobutyl)alumoxane(TIBAO),tetra-(2,4,4-trimethyl-pentyl)alumoxane(TIOAO),tetra-(2,3-dimethylbutyl)alumoxane(TDMBAO) andtetra-(2,3,3-trimethylbutyl)alumoxane(TTMBAO). Particularly interestingalumoxanes are those described in WO 99/21899 and in WO01/21674 in whichthe alkyl and aryl groups have specific branched patterns.

Non-limiting examples of aluminium compounds according to WO 99/21899and WO01/21674 are:

tris(2,3,3-trimethyl-butyl)aluminium, tris(2,3-dimethyl-hexyl)aluminium,tris(2,3-dimethyl-butyl)aluminium, tris(2,3-dimethyl-pentyl)aluminium,tris(2,3-dimethyl-heptyl)aluminium,tris(2-methyl-3-ethyl-pentyl)aluminium,tris(2-methyl-3-ethyl-hexyl)aluminium,tris(2-methyl-3-ethyl-heptyl)aluminium,tris(2-methyl-3-propyl-hexyl)aluminium,tris(2-ethyl-3-methyl-butyl)aluminium,tris(2-ethyl-3-methyl-pentyl)aluminium,tris(2,3-diethyl-pentyl)aluminium,tris(2-propyl-3-methyl-butyl)aluminium,tris(2-isopropyl-3-methyl-butyl)aluminium,tris(2-isobutyl-3-methyl-pentyl)aluminium,tris(2,3,3-trimethyl-pentyl)aluminium,tris(2,3,3-trimethyl-hexyl)aluminium,tris(2-ethyl-3,3-dimethyl-butyl)aluminium,tris(2-ethyl-3,3-dimethyl-pentyl)aluminium,tris(2-isopropyl-3,3-dimethyl-butyl)aluminium,tris(2-trimethylsilyl-propyl)aluminium,tris(2-methyl-3-phenyl-butyl)aluminium,tris(2-ethyl-3-phenyl-butyl)aluminium,tris(2,3-dimethyl-3-phenyl-butyl)aluminium,tris(2-phenyl-propyl)aluminium,tris[2-(4-fluoro-phenyl)-propyl]aluminium,tris[2-(4-chloro-phenyl)-propyl]aluminium,tris[2-(3-isopropyl-phenyl)-propyl]aluminium,tris(2-phenyl-butyl)aluminium, tris(3-methyl-2-phenyl-butyl)aluminium,tris(2-phenyl-pentyl)aluminium,tris[2-(pentafluorophenyl)-propyl]aluminium,tris[2,2-diphenyl-ethyl]aluminium andtris[2-phenyl-2-methyl-propyl]aluminium, as well as the correspondingcompounds wherein one of the hydrocarbyl groups is replaced with ahydrogen atom, and those wherein one or two of the hydrocarbyl groupsare replaced with an isobutyl group.

Amongst the above aluminium compounds, trimethylaluminium (TMA),triisobutylaluminium (TIBAL), tris(2,4,4-trimethyl-pentyl)aluminium(TIOA), tris(2,3-dimethylbutyl)aluminium (TDMBA) andtris(2,3,3-trimethylbutyl)aluminium (TIMBA) are preferred.

Non-limiting examples of compounds able to form an alkylmetallocenecation are compounds of formula D⁺E⁻, wherein D⁺ is a Bronsted acid,able to donate a proton and to react irreversibly with a substituent Xof the metallocene of formula (I) and E is a compatible anion, which isable to stabilize the active catalytic species originating from thereaction of the two compounds, and which is sufficiently labile to beable to be removed by an olefinic monomer. Preferably, the anion E⁻comprises of one or more boron atoms. More preferably, the anion E⁻ isan anion of the formula BAr₄ ⁽⁻⁾, wherein the substituents Ar which canbe identical or different are aryl radicals such as phenyl,pentafluorophenyl or bis(trifluoromethyl)phenyl.Tetrakis-pentafluorophenyl borate is particularly preferred examples ofthese compounds are described in WO 91/02012. Moreover, compounds of theformula BAr₃ can conveniently be used. Compounds of this type aredescribed, for example, in the published International patentapplication WO 92/00333. Other examples of compounds able to form analkylmetallocene cation are compounds of formula BAr₃P wherein P is asubstituted or unsubstituted pyrrol radicals. These compounds aredescribed in WO01/62764. Other examples of cocatalyst can be found in EP775707 and DE 19917985. Compounds containing boron atoms can beconveniently supported according to the description of WO 01/47635 andWO 01/48035. All these compounds containing boron atoms can be used in amolar ratio between boron and the metal of the metallocene comprisedbetween about 1:1 and about 10:1; preferably 1:1 and 2.1; morepreferably about 1:1.

Non limiting examples of compounds of formula D⁺E⁻ are:

Triethylammoniumtetra(phenyl)borate,

Tributylammoniumtetra(phenyl)borate,

Trimethylammoniumtetra(tolyl)borate,

Tributylammoniumtetra(tolyl)borate,

Tributylammoniumtetra(pentafluorophenyl)borate,

Tributylammoniumtetra(pentafluorophenyl)aluminate,

Tripropylammoniumtetra(dimethylphenyl)borate,

Tributylammoniumtetra(trifluoromethylphenyl)borate,

Tributylammoniumtetra(4-fluorophenyl)borate,

N,N-Dimethylbenzylammonium-tetrakispentafluorophenylborate,

N,N-Dimethylhexylamonium-tetrakispentafluorophenylborate,

N,N-Dimethylaniliniumtetra(phenyl)borate,

N,N-Diethylaniliniumtetra(phenyl)borate,

N,N-Dimethylaniliniumtetrakis(pentafluorophenyl)borate,

N,N-Dimethylaniliniumtetrakis(pentafluorophenyl)aluminate,

N,N-Dimethylbenzylammonium-tetrakispentafluorophenylborate,

N,N-Dimethylhexylamonium-tetrakispentafluorophenylborate,

Di(propyl)ammoniurntetrakis(pentafluorophenyl)borate,

Di(cyclohexyl)ammoniumtetrakis(pentafluorophenyl)borate,

Triphenylphosphoniumtetrakis(phenyl)borate,

Triethylphosphoniumtetrakis(phenyl)borate,

Diphenylphosphoniumtetrakis(phenyl)borate,

Tri(methylphenyl)phosphoniumtetradis(phenyl)borate,

Tri(dimethylphenyl)phosphoniumtetrakis(phenyl)borate,

Triphenylcarbeniumtetrakis(pentafluorophenyl)borate,

Triphenylcarbeniumtetralis(pentafluorophenyl)aluminate,

Triphenylcarbeniumtetradis(phenyl)aluminate,

Ferroceniumtetrakis(pentafluorophenyl)borate,

Ferroceniumtetrakis(pentafluorophenyl)aluminate.

Triphenylcarbeniumtetrakis(pentafluorophenyl)borate, and

N,N-Dimethylaniliniumtetrakis(pentafluorophenyl)borate.

Organic aluminum compounds used as compound c) are those of formulaH_(j)AlU_(3-j) or H_(j)Al₂U_(6-j) described above.

The catalysts system used in the process of the present invention canalso be supported on an inert carrier. This is achieved by depositingthe metallocene compound a) or the product of the reaction thereof withthe component b), or the component b) and then the metallocene compounda) on an inert support such as, for example, silica, alumina, Al-Si,Al-Mg mixed oxides, magnesium halides, styrene/divinylbenzenecopolymers, polyethylene or polypropylene. The supportation process iscarried out in an inert solvent such as an hydrocarbon (for exampletoluene, hexane, pentane or propane) at a temperature ranging from 0° C.to 100° C. and preferably at a temperature ranging from 25° C. to 90° C.

A suitable class of inert supports is constituted by porous organicsupports functionalized with groups having active hydrogen atoms.Particularly suitable are those in which the organic support is apartially crosslinked styrene polymer. Supports of this type aredescribed in European application EP-633 272.

Another class of inert supports particularly suitable for use accordingto the invention is that of polyolefin porous prepolymers, particularlypolyethylene.

A further suitable class of inert supports for use according to theinvention is that of porous magnesium halides, such as those describedin International application WO 95/32995.

The solid compound thus obtained, optionally in combination withalkylaluminium compound, either as such or prereacted with water, can beusefully employed in gas-phase polymerization. The process for thepolymerization of olefins according to the invention can be carried outin the liquid phase, in the presence or absence of an inert hydrocarbonsolvent, or in the gas phase. The hydrocarbon solvent can either bearomatic such as toluene, or aliphatic such as propane, hexane, heptane,isobutane or cyclohexane.

The polymerization temperature is generally comprised between −100° C.and +100° C. and, particularly between 10° C. and +90° C. Thepolymerization pressure is generally comprised between 0,5 and 100 bar.

The lower the polymerization temperature, the higher are the resultingmolecular weights of the polymers obtained.

The polymerization yields depend on the purity of the metallocenecompound of the catalyst system. The metallocene compounds obtained bythe process of the invention can therefore be used as such or can besubjected to purification treatments.

The components of the catalyst system can be brought into contact witheach other before the polymerization. The pre-contact concentrations aregenerally between 0.1 and 10⁻⁸ mol/l for the metallocene component a),while they are generally between 2 and 10⁻⁸ mol/l for the component b).The pre-contact is generally effected in the presence of a hydrocarbonsolvent and, if appropriate, of small quantities of monomer. In thepre-contact it is also possible to use a non-polymerizable olefin, suchas isobutene, 2-butene and the like.

The molecular weight distribution can be varied by using mixtures ofdifferent metallocene compounds or by carrying out the polymerization inseveral stages which differ as to the polymerization temperature and/orthe concentrations of the molecular weight regulators and/or themonomers concentration. Moreover, by carrying out the polymerizationprocess by using a combination of two different metallocene compounds offormula (I), a polymer endowed with a broad molecular weightdistribution is produced.

In the copolymers obtainable by the process of the invention, thecontent of ethylene derived units is between 99.9% by mol and 1% by mol;preferably is it between 99% by mol and 70% by mol; and more preferablyit is between 95% by mol and 60% by mol.

The content of aplha-olefins derived units is between 0.1% by mol and99% by mol; preferably is it between 1% by mol and 30% by mol; and morepreferably it is between 5% by mol and 40% by mol.

Non-limiting examples of alpha-olefins of formula CH₂═CHA which can beused as alpha-olefins in the process of the invention are 1-butene,1-pentene, 4-methyl-l-pentene, 1-hexene, 1-octene,4,6-dimethyl-1-heptene, 1-decene, 1-dodecene, 1-tetradecene,1-hexadecene, 1-octadecene and 1-eicosene. Preferred comonomers are1-pentene, 1-hexene and 1-octene.

The content of polyene derived units is preferably comprised between 0%and 5% by mol and, more preferably between 0 and 3 by mol %.

The polyenes that can be used as comonomers in the copolymers accordingto the present invention are included in the following classes:

-   -   non-conjugated diolefins able to cyclopolymerize such as, for        example, 1,5-hexadiene, 1-6-heptadiene, 2-methyl-1,5-hexadiene;    -   dienes capable of giving unsaturated monomeric units, in        particular conjugated dienes such as, for example, butadiene and        isoprene, and linear non-conjugated dienes, such as, for        example, trans 1,4-hexadiene, cis 1,4-hexadiene,        6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene,        11-methyl-1,10-dodecadiene, and cyclic non-conjugated dienes        such as 5-ethylidene-2-norbornene.

With a process of the present invention it is possible to achieve a goodbalance of different properties. In fact, with the process of thepresent invention the incorporation of the comonomer is high and thisallows the use of a smaller excess of comonomer in the reactor and toachieve e better tunable process. At the same time the comonomer is welldistributed, as shown by the r1×r2 values and by the glass transitiontemperature. Moreover the copolymers obtained with the process of thepresent invention have a high molecular weight (I.V.) that makes theprocess object of the present invention suitable for an industrial use.

The intrinsic viscosity values are generally higher than 0.5 dL/g,preferably they are between from 1.5 to 10 dL/g; and more preferablybetween 2 and 4 dL/g.

The following examples are given for illustrative purposes and do notintend to limit the invention.

EXAMPLES

General Procedures

All operations were performed under nitrogen by using conventionalSchlenk-line techniques. Heptane and toluene were purified by degassingwith N₂ and passing over activated (8 hours, N₂ purge, 300° C.) Al₂O₃,and stored under nitrogen. 1-hexene (Aldrich) was dried over alumina anddistilled over LiAl₄. Polymerization grade ethylene was obtained fromthe Basell Ferrara plant. MAO (methylalumoxane, Witco) was purchased asa 10 wt.-% solution in toluene, dried under vacuum to remove most of thefree trimethylaluminuim and used as 1 M toluene solution. TIBA(Al(i-Bu)₃, Witco) was used as 1 M toluene solution.

¹H NMR spectra of copolymers were recorded at 120° C. on a BrukerDPX-400 spectrometer operating at 100.61 MHz, in the Fourier transformmode. The samples were prepared by dissolving 10 mg of copolymer in 0.5mL of 1,1,2,2-tetrachloroethane-d₂ at 120° C. The peak of C₂HDCl₂ (5.95ppm) was used as internal standard. Each spectrum was acquired with a45° pulse and 20 seconds of delay between pulses. About 16 transientswere stored in 32K data points using a spectral window of 16 ppm.

The 1-hexene content in the copolymers was calculated from the methyleneand methyne peak integral (I_(A)) and the methyl peak integral (I_(B)),by applying the following relationships:[C ₆ ]=I _(B)/38 C ₂]=(I _(A)-3I _(B))/4Σ=[C ₆ ]+[C ₂]=(I _(B)/3)+(I _(A)-3I _(B))/4C _(6 copol) (% mol)=100×[C ₆]/Σ=100×I _(B)/3Σ

The molecular weight distribution was determined on a WATERS 150 C usingthe following chromatographic conditions: Columns: 3× SODEX AT 806 MS;1× SODEX UT 807; 1× SODEX AT-G; Solvent: 1,2,4 trichlorobenzene (+0.025%2,6-di-tert-butyl-4-methyl-phenol) Flow rate: 0.6-1 mL/min Temperature:135° C. Detector: Infrared at λ ≅ 3.5 μm

Calibration:Universal Calibration with PS-Standard

The intrinsic viscosity (I.V.) was measured in decaline (DHN) at 135° C.

The melting points (T_(m)) and glass transition temperatures (T_(g))were determined on a DSC30 Mettler instrument equipped with a coolingdevice, by heating the sample from 25° C. to 200° C at 20° C./min,holding for 10 min at 200° C., cooling from 200° C. to −140° C., holdingfor 2 min at −140° C., heating from −140° C. to 200° C. at 20° C./min.The reported values are those determined from the second heating scan.

In cases in which crystallization phenomena overlap with the glasstransition, for a better determination of the T_(g) value, the sampleswere heated to 200° C. at 20° C./minute, quickly cooled to a temperaturelower than the T_(m) (usually 20, 0 or −20° C.) at 200° C./minute, andkept at this temperature for 720 minutes. The samples were then furtherquickly cooled to −140° C. at 200° C./minute and finally re-heated to200° C. at 20° C./minute. The whole process was carried out undernitrogen flow of 20 mL/minute.

Determination of Liquid Phase Composition

The liquid phase composition was calculated from the Redlich-Kwong-Soaveequations. This set of thermodynamic equations was selected among thoseavailable in Aspen Plus™ (commercialized by Aspen Technology Inc.,Release 9) on the basis of a comparison with the experimental results.The concentrations of the comonomers were hence calculated.

Metallocene Compounds

Dimethylsilylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride [C1]

was prepared according to U.S. Pat. No. 5,786,432.

dimethylsilylbis(2-methyl-4(4-tertbutyl-phenyl)-1-indenyl)zirconiumdichloride [A1]

was prepared according to WO 98/40331

POLYMERIZATION EXAMPLES 1-6

General Procedure

Ethylene/1-hexene copolymerizations were carried out in a 260-mL Büchiglass autoclave equipped with magnetic stirrer, thermocouple and feedingline for the monomer, purified with nitrogen and kept in a thermostaticbath. Heptane and 1-hexene (150 mL of total volume, amount of 1-hexeneis reported in table 1 ), and trisobutylaluminum (TIBA) (0.5 mmol) wereintroduced and warmed to 70° C., then the autoclave was purged withethylene. The catalytic system was separately prepared in 5 mL oftoluene by mixing the amounts of metallocene reported in table 1 andmethylalumoxane (MAO) (MAO/Zr ratio 500 mol/mol). After about 30 sec ofstirring at room temperature, the solution was introduced into theautoclave under ethylene flow. The reactor was closed and pressurizedwith ethylene at 4 bar-g; the temperature was raised at 70° C. and thepressure was kept constant by feeding in ethylene. The polymerizationwas stopped after the time indicate in table 1 by degassing the reactorand by adding 2 mL of methanol. The polymer was precipitated with 200 mLof acetone, filtered, washed with acetone and dried overnight at 60° C.under reduced pressure. Polymerization conditions and polymer data arereported in table 1. TABLE 1 1- 1-hexene liquid Activity 1-hex copolamount hexene phase Time Yield Kg_(Pol)/ (¹H NMR) I.V. T_(g) T_(m) Exmetall. μmol (g) (% mol) (% wt) (min) (g) (mmol_(Zr)*h) (% mol) r₁ × r₂(dL/g) Mw/Mn ° C. ° C. 1* C1 0.2 1.32 22.8 46.9 5 0.5 30.6 10.3 1.222.96 2.48 −44.3 82.5 2* C1 0.3 3.29 42.4 68.8 5 1.3 51.2 21.5 0.94 2.172.39 −51.3 n.d. 3* C1 0.3 6.59 59.3 81.4 7 1.1 30.3 32.6 0.99 1.72 2.51−56.0 n.d. 4 A1 0.3 1.32 22.8 46.9 3 1.0 66.0 15.8 0.80 2.8 2.59 −51.656.6 5 A1 0.3 3.29 42.4 68.8 5 1.1 43.6 26.5 0.69 2.27 2.49 −57.1 n.d. 6A1 0.3 6.59 59.3 81.4 5 0.8 31.2 32.3 0.82 1.92 2.46 −58.2 n.d.*comparative examplesn.d. = not determinable;

1. A process for producing a polymer of ethylene containing from 0.1 to99% by mol of derived units of at least one alpha-olefin of formulaCH₂═CHA, wherein A is a C₂-C₂₀ alkyl radical and optionally up to 5% bymol polyene, comprising contacting, under polymerization conditions,ethylene, at least one alpha-olefin and optionally said polyene, in thepresence of a catalyst system obtained by contacting: a) a metallocenecompound of formula (I):

wherein M is zirconium, titanium or hafnium; X, equal to or differentfrom each other, is a hydrogen atom, a halogen atom, a R, OR, OR′O,OSO₂CF₃, OCOR, SR, NR₂ or PR₂ group, wherein the R substituents arelinear or branched, saturated or unsaturated C₁-C₂₀-alkyl,C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkylradicals, optionally containing at least one heteroatom belonging togroups 13-17 of the Periodic Table of the Elements; and theR′substituent is a C₁-C₄₀-alkylidene, C₆-C₄₀-arylidene,C₇-C₄₀-alkylarylidene or C₇-C₄₀-arylalkylidene; R¹ , equal to ordifferent from each other, are a linear or branched C₁-C₂₀-alkylradical; R², equal to or different from each other, is a hydrogen atomor a linear or branched, saturated or unsaturated C₁-C₂₀-alkyl radical;R³ and R⁴, equal to or different from each other, are hydrogen atoms orlinear or branched, saturated or unsaturated C₁-C₂₀-alkyl,C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkylradicals, optionally containing at least one heteroatom belonging togroups 13-17 of the Periodic Table of the Elements; or they can formtogether a condensed saturated or unsaturated 5 or 6 membered ring,optionally containing at least one heteroatom belonging to groups 13-16of the Periodic Table of the Elements, said ring optionally bearing atleast one substituent; R⁵ and R⁶, equal to or different from each other,are hydrogen atoms or linear or branched, saturated or unsaturatedC₁-C₂₀-alkyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl orC₇-C₂₀-arylalkyl radicals, optionally containing at least one heteroatombelonging to groups 13-17 of the Periodic Table of the Elements; or theycan form together a condensed saturated or unsaturated 5 or 6 memberedring, optionally containing at least one heteroatom belonging to groups13-16 of the Periodic Table of the Elements, said ring optionallybearing at least one substituent; Q is a radical of formula (II) whichis bonded to the indenyl at the position marked by the symbol *;

wherein T¹, T², T³, T⁴ and T⁵, same or different, are carbon atoms (C)or nitrogen atoms (N); m¹, m², m³, m⁴ and m⁵ are or 1; ml, m², m³, m⁴and m⁵ being 0 when the correspondent T¹, T², T³, T⁴ and T⁵ is anitrogen atom, and being 1 when the correspondent T¹, T², T³, T⁴ and T⁵is a carbon atom; R⁷, R⁸, R⁹, R¹⁰ and R¹¹, equal to or different fromeach other, are hydrogen atoms or linear or branched, saturated orunsaturated C₁-C₂₀-alkyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl,C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkyl radicals, optionally containing atleast one heteroatom belonging to groups 13-17 of the Periodic Table ofthe Elements; or they can form together a condensed saturated orunsaturated 5 or 6 membered ring, optionally containing at least oneheteroatom belonging to groups 13-16 of the Periodic Table of theElements; said rings can bear at least one substituent; with theprovisos that at least one of R⁷, R⁸, R⁹, R¹⁰ and R¹¹ is different fromhydrogen atom, and that no more than two of T¹, T², T³, T⁴ and T⁵ arenitrogen atoms; and b) an alumoxane or a compound that forms an alkylmetallocene cation.
 2. The process according to claim 1 wherein thecatalyst system further comprises an organo aluminum compound.
 3. Theprocess according to claim 1 wherein in the compound of formula (I), Xis a halogen atom, a R, OR′O or OR group R³ and R⁴ are hydrogen atoms,methyl or they form a condensed saturated or unsaturated 5 or 6 memberedring; and R and R⁶ are C₁-C₂₀-alkyl or C₆-C₂₀-aryl radicals.
 4. Theprocess according to claim 1 wherein in the radical of formula (II), R⁹is a linear or branched, saturated or unsaturated C₁-C₂₀-alkyl,C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkylradicals; and R⁷, R⁸, R¹⁰ and R¹¹ are hydrogen atoms.
 5. The processaccording to claim 1 wherein in the radical of formula (II), R⁸ and R¹⁰are a linear or branched, saturated or unsaturated C₁-C₂₀-alkyl,C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl, C₇-C₂₀-arylalkylradicals; and R⁷, R⁹ and R¹¹ are hydrogen atoms.
 6. The processaccording to claim 4 wherein the radical belonging to formula (II) hasformula (IIa), being bonded to the indenyl at the position indicated bythe symbol *:

wherein R⁹ is a branched, saturated or unsaturated C₁-C₂₀-alkyl orC₆-C₂₀-aryl radical.
 7. The process according to claim 6 wherein R⁹ is aphenyl group, optionally substituted with at least one C₁-C₁₀ alkylgroup or a group of formula C(R¹²)₃ wherein R¹², same or different, is alinear or branched, saturated or unsaturated C₁-C₆-alkyl radical.
 8. Theprocess according to claim 1 wherein the radical belonging to formula(II) has formula (IIb), being bonded to the indenyl at the positionindicated by the symbol *

wherein R⁸ and R¹⁰, are a branched, saturated or unsaturatedC₁-C₂₀-alkyl or a CF₃ radical; R⁹ is a hydrogen atom or a linear orbranched, saturated or unsaturated C₁-C₂₀-alkyl or C₆-C₂₀-aryl radical,optionally containing at least one heteroatom belonging to groups 13-17of the Periodic Table of the Elements.
 9. The process according to claim8 wherein R⁸ and R¹⁰ are a group of formula C(R¹²)₃ wherein R¹², same ordifferent, is a linear or branched, saturated or unsaturated C₁-C₆-alkylradical and R⁹ is a hydrogen atom.
 10. The process according to claim 1wherein the radical belonging to formula (II) has formula (IIc), beingbonded to the indenyl at the position indicated by the symbol *:

wherein at least one among R⁸, R⁹, R¹⁰ and R¹¹ is different from ahydrogen atom.
 11. The process according to claim 10 wherein R¹⁰ and R¹¹are hydrogen atoms; R⁸ and R⁹ are a linear or branched, saturated orunsaturated C₁-C₂₀-alkyl radical, or form a saturated or unsaturatedcondensed 5 or 6 membered ring optionally containing at least oneheteroatom belonging to groups 13-16 of the Periodic Table of theElements, said ring optionally bearing at least one substituent.
 12. Theprocess according to claim 1 wherein the radical belonging to formula(II) has formula (IId) being bonded to the indenyl at the positionindicated by the symbol *:

wherein R¹⁰ and R¹¹ are a linear or branched, saturated or unsaturatedC₁-C₂₀-alkyl radical, or form a saturated or unsaturated condensed 5 or6 membered ring optionally containing at least one heteroatom belongingto groups 13-16 of the Periodic Table of the Elements, said ringoptionally bearing at least one substituent.
 13. The process accordingto claim 1 wherein the alpha-olefin is 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene, 4,6-dimethyl-1-heptene,1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene or1-eicosene.
 14. The process according to claim 13 wherein thealpha-olefin is 1-pentene, 1-hexene or 1-octene.